Expression of genes encoding neuropeptides and enzymes in the brain, with emphasis on the hypothalamus, are being studied. We successfully created a knock-out of the oxytocin gene in mice through homologous recombination. These mice demonstrate that oxytocin is absolutely required for milk ejection, but not mammary gland development, fertility or parturition. We are conducting further studies to see how the absence of oxytocin affects mouse behavior and reproduction. Initial studies indicate that some aspects of aggressive behavior are decreased. We have determined that oxytocin participates in the regulation of mammary gland celllular development and apoptosis. Finally, we have determined how to use the OT gene to express in a cell-specific way foreign genes in the mouse brain. This past year, we also investigated the stem cell lines and chimeric mice that were created to make knock-outs of the oxytocin receptor (OTR). We find that the trait is not passsed along to heterozygote mice. We believe that this is due to the necessity for this receptor on the germ cells. Attempts to circumvent this block are under pursuit. This past year, we have also generated heterozygotes for the vasopressin 1b receptor knock-out. They are currently being bred to homozygosity in anticipation of intense study. We have also cloned a suspected gene for a vasopressin metabolite receptor. We will investigate further the function of this clone, thought to be involved in memory. We used the technique of differential display to isolate the genes from pineal gland. One novel gene, PG10.2, was also found expressed in the retina humans. We determined its chromosomal location and suggested it as a candidate gene for the Bardet-Beidl Syndrome, an autosomal recessive disorder characterized by mental retardation, obesity, retinitis pigmentosa, polydactyly and hypogonadism. Mapping of gene expression in the human hypothalamus continues: analyses of vasopressin, oxytocin, LHRH, substance P, neurokinin B and the opioids have been published. Maps of the corticotropin-releasing factor, somatostatin, and growth hormone-releasing factor are in progress.